I. Field of the Invention
This invention relates generally to catheters used in sensing electrical activity within a patient and administering therapy, and more particularly to such catheters incorporating deposited thin film electrodes thereon for improved flexibility and trackability within the body.
II. Discussion of the Prior Art
A recognized procedure used in treating various cardiac arrhythmias involves ablating cardiac tissue at an appropriate site to block aberrant re-entrant paths. In a normal heart, the sino-atrial node located in right atrium depolarizes on a cyclic basis and a resulting electrical wave propagates to the AV node causing it to fire and send a further electrical wave down the bundle of His and there along the left and right bundle branches to produce a coordinated contraction of the ventricles. Arrhythmia, including atrial fibrillation, atrial flutter and tachycardia often results when the heart's normal conduction system includes a re-entrant path from the ventricles to the atrium, resulting in the feedback of electrical impulses that mix with depolarizations of the S-A node to deliver erratic signals to the A-V node.
In addressing these arrhythmias, procedures referred to as electrophysiology mapping and ablation electrophysiological therapy are used. In carrying out such therapy, a physician will first steer a catheter having sensing/ablation electrodes on the distal end thereof through the patient's vascular system and into a predetermined chamber of the heart where the treatment is to be carried out. The catheter is manipulated so as to place the electrodes into direct contact with the myocardial tissue that is sensed and/or to be ablated. Sensing and/or ablation can be performed on the endocardial surface or via coronary veins and arteries. The aberrant path and/or ectopic foci is first located using a "mapping" technique in which cardiac depolarization signals picked up by the electrodes are transmitted over electrical conductors in the lead to a suitable monitor/analyzer. When an aberrant conductive pathway or an ectopic foci is located, the physician positions the electrodes so that predetermined ones are in direct contact with the myocardial tissue to be ablated. The physician then activates a voltage generator, usually a source of RF voltage connected across a pair of electrodes, to effectively ablate and form a line of scar tissue interrupting the aberrant conductive pathway or to eliminate the ectopic foci.
Those desiring additional information relating to the use of ablation/mapping catheters for treating cardiac arrhythmias are referred to "Catheter Ablation of the Atrioventricular Junction with Radiofrequency Energy" by Landberg et al., Circulation, Vol. 80, No. 6, December 1989, "Radiofrequency Catheter Ablation of Atrial Arrhythmias" , by Lesh et al., Circulation, Vol. 89, No. 3, March 1994, and "Efficacy of Radiofrequency Ablation of Atrial Tissue in Common Atrial Flutter", by Kirkorian et al., NASPE, May 1993. The use of electrode carrying catheters for ablating locations within a heart chamber is also disclosed in U.S. Pat. Nos. 4,641,649; 4,892,102; and 5,025,786.
The prior art further discloses a number of different electrode configurations. In the Fleischhacker et al. U.S. Pat. No. 5,676,662, a conductive wire helix is wrapped about an elongated polymer catheter body where certain portions of the turns of the helix are uncoated so as to expose bare metal that forms the electrode surfaces. In the Swanson et al. U.S. Pat. No. 5,582,609 discrete helical windings are disposed near the distal end of an elongated flexible plastic catheter. The helical winding is intended to provide increased flexibility for allowing the catheter to better conform to the surface of the tissue to be ablated. In the Pomeranz et al. U.S. Pat. No. 5,558,073, the electrodes each comprise a metallic ring disposed about the circumference of the catheter body. A plurality of electrical conductors extend through a lumen of the catheter body to connect the metallic rings to terminals at the proximal end of the catheter body. Such ring electrodes are also shown in the Truckai et al. U.S. Pat. No. 5,487,757. In the prior art arrangements, the ring electrodes are typically preformed bands of metal that are adhesively bonded, crimped or otherwise attached to the exterior surface of the catheter body, and which are connected by electrical conductors that extend through one or more lumens in the catheter body to connectors at its proximal end. These rings tend to be relatively thick and are therefor rigid. When it is considered that up to ten such ring electrodes are typically spaced about one centimeter apart along the distal end portion of the catheter body, they impact the ability of the distal end portion of the catheter to flex and conform to tissue structures to be mapped/ablated.
Leads constructed in accordance with the present invention can find use not only in mapping the endocardium and ablating tissue to treat cardiac arrhythmias, but also can be used in fabricating pacing and defibrillating leads as well as neurologic leads placed along the spinal column by which electrical stimulation can be applied to the body for treating chronic pain.
It is a principal purpose of the present invention to provide an improved electrophysiology catheter that exhibits improved flexibility when contrasted with known prior art mapping and ablation catheters. Rather than using a plurality of solid, preformed, tubular, metal ring electrodes, we instead deposit multiple layers of different metals as thin films so that the resulting multilayer structure may have a thickness between 5 and 250 microns, but with between 5 and 20 microns being preferred. With such thin electrodes, they are able to readily flex and do not detract from the overall flexibility of the distal end portion of the catheter. Moreover, they can be configured in various shapes and patterns to optimize tissue contact.
Historically, thin metallic films have not been suitable for use as conductive electrodes on flexible polymers, although efforts to do so have been attempted. Past efforts have been plagued with a number of problems including: (1) being able to adhere the thin metal film coating to the polymer substrate, especially on flexure thereof; (2) lack of adhesion of the coating to itself (internal adhesion) as the coating is oxidized by air; (3) formation of cracks emanating in the film which lead to either loss of conductivity or undesirable "spark gaps"; (4) temperature build-up in the film resulting from internal micro-cracks which overwhelm the minimal heat capacity of a metal that is less than 1 mil thick; and (5) inherent stresses that exist in a columnar structured film as it is longitudinally stretched. Because of the aforementioned problems, persons skilled in the art of designing and producing electrical leads/catheters have stayed away from the use of thin films even though such thin film electrodes offer significant advantages, especially enhanced flexibility and improved configuration to optimize contact along an interior surface of a body cavity, and greater energy transfer because such films have no thermal capacity and, hence, no heating occurs of the film itself. As such, there is no loss of energy in the thermal heating of the thin film ring electrode.